A light emitting diode is a p-n junction diode having a characteristic of converting electric energy into light energy. The p-n junction diode can be formed of compound semiconductors including Group III and V elements of the periodic table. The LED can represent various colors by adjusting the compositional ratio of compound semiconductors.
When forward voltage is applied to the light emitting diode, electrons of an p-layer are combined with holes of a p-layer, so that energy corresponding to an energy gap between a conduction band and a valance band is generated. If the energy is realized as light, the light emitting diode emits the energy in the form of light.
Nitride semiconductors attract a great attention in the optical device and high-power electronic device development fields because of their high thermal stability and wide band gap energy. In particular, blue, green and UV light emitting diodes using nitride semiconductors have been commercialized and widely used.
A conventional light emitting diode can be classified into a lateral type light emitting diode and a vertical type light emitting diode according to positions of electrodes. In both of the lateral type light emitting diode and the vertical type light emitting diode, light generated at a lower portion of a pad electrode does not escape to the outside but is absorbed into a pad, or is reflected into a semiconductor at a lower portion of the pad, and therefore, light extraction efficiency is deteriorated. Hence, a current blocking layer (CBL) is provided at a lower portion of the pad.
However, a light emitting area is decreased by the CBL, and a current concentration phenomenon still occurs in a region close to the electrode.